Credit: The Associated Press

In this Dec. 8, 2012 file photo, Chinese paramilitary policemen build a fence near a concrete marker depicting the North Korean and Chinese national flags with the words "China North Korea Border" at a crossing in the Chinese border town of Tumen in eastern China's Jilin province.

BEIJING — China is trying to punish ally North Korea for its nuclear and missile tests, stepping up inspections of North Korean-bound cargo in a calibrated effort to send a message of Chinese pique without further provoking a testy Pyongyang government.